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Background: Mitochondria have an essential role in regulating metabolism and integrate environmental and physiological signals to affect processes such as cellular bioenergetics and response to stress. In the metabolically active skeletal muscle, mitochondrial biogenesis is one important component contributing to a broad set of mitochondrial adaptations occurring in response to signals, which converge on the biogenesis transcriptional regulator peroxisome proliferator-activated receptor coactivator 1-alpha (PGC-1α), and is central to the beneficial effects of exercise in skeletal muscle. We investigated the role of long non-coding RNA (lncRNA) taurine-upregulated gene 1 (TUG1), which interacts with PGC-1α in regulating transcriptional responses to exercise in skeletal muscle. Results: In human skeletal muscle, TUG1 gene expression was upregulated post-exercise and was also positively correlated with the increase in PGC-1α gene expression (PPARGC1A). Tug1 knockdown (KD) in differentiating mouse myotubes led to decreased Ppargc1a gene expression, impaired mitochondrial respiration and morphology, and enhanced myosin heavy chain slow isoform protein expression. In response to a Ca2+-mediated stimulus, Tug1 KD prevented an increase in Ppargc1a expression. RNA sequencing revealed that Tug1 KD impacted mitochondrial Ca2+ transport genes and several downstream PGC-1α targets. Finally, Tug1 KD modulated the expression of ~300 genes that were upregulated in response to an in vitro model of exercise in myotubes, including genes involved in regulating myogenesis. Conclusions: We found that TUG1 is upregulated in human skeletal muscle after a single session of exercise, and mechanistically, Tug1 regulates transcriptional networks associated with mitochondrial calcium handling, muscle differentiation and myogenesis. These data demonstrate that lncRNA Tug1 exerts regulation over fundamental aspects of skeletal muscle biology and response to exercise stimuli. [ABSTRACT FROM AUTHOR]

Insulin infusion increases skeletal muscle microvascular blood flow (MBF) in healthy people but is impaired during insulin resistance. However, we have shown that eliciting insulin secretion via oral glucose loading in healthy people impairs muscle MBF, whilst others have demonstrated intravenous glucose infusion stimulates MBF. We aimed to show that the route of glucose administration (oral versus intravenous) influences muscle MBF, and explore potential gut‐derived hormones that may explain these divergent responses. Ten healthy individuals underwent a 120 min oral glucose tolerance test (OGTT; 75 g glucose) and on a subsequent occasion an intravenous glucose tolerance test (IVGTT, bypassing the gut) matched for similar blood glucose excursions. Femoral artery and thigh muscle microvascular (contrast‐enhanced ultrasound) haemodynamics were measured at baseline and during the OGTT/IVGTT. Plasma insulin, C‐peptide, glucagon, non‐esterified fatty acids and a range of gut‐derived hormones and incretins (gastric inhibitory polypeptide (GIP) and glucagon‐like peptide‐1(GLP‐1)) were measured at baseline and throughout the OGTT/IVGTT. The IVGTT increased whereas the OGTT impaired MBF (1.3‐fold versus 0.5‐fold from baseline, respectively, P = 0.0006). The impairment in MBF during the OGTT occurred despite producing 2.8‐fold higher plasma insulin concentrations (P = 0.0001). The change in MBF from baseline (ΔMBF) negatively correlated with ΔGIP concentrations (r = −0.665, P < 0.0001). The natural log ratio of incretins GLP‐1:GIP was positively associated with ΔMBF (r = 0.658, P < 0.0001), suggesting they have opposing actions on the microvasculature. Postprandial hyperglycaemia per se does not acutely determine opposing microvascular responses between OGTT and IVGTT. Incretins may play a role in modulating skeletal muscle MBF in humans. Key points: Insulin or mixed nutrient meals stimulate skeletal muscle microvascular blood flow (MBF) to aid in the delivery of nutrients; however, this vascular effect is lost during insulin resistance.Food/drinks containing large glucose loads impair MBF in healthy people; however, this impairment is not observed when glucose is infused intravenously (bypassing the gut).We investigated skeletal muscle MBF responses to a 75 g oral glucose tolerance test and intravenous glucose infusion and aimed to identify potential gut hormones responsible for glucose‐mediated changes in MBF.Despite similar blood glucose concentrations, orally ingested glucose impaired, whereas intravenously infused glucose augmented, skeletal muscle MBF. The incretin gastric inhibitory polypeptide was negatively associated with MBF, suggestive of an incretin‐mediated MBF response to oral glucose ingestion.This work provides new insight into why diets high in glucose may be detrimental to vascular health and provides new avenues for novel treatment strategies targeting microvascular dysfunction. [ABSTRACT FROM AUTHOR]

Key points: Exercise, insulin‐infusion and low‐glucose mixed‐nutrient meal ingestion increases muscle microvascular blood flow which in part facilitates glucose delivery and disposal. In contrast, high‐glucose ingestion impairs muscle microvascular blood flow which may contribute to impaired postprandial metabolism.We investigated the effects of prior cycling exercise on postprandial muscle microvascular blood flow responses to a high‐glucose mixed‐nutrient meal ingested 3 and 24 h post‐exercise.Prior exercise enhanced muscle microvascular blood flow and mitigated microvascular impairments induced by a high‐glucose mixed meal ingested 3 h post‐exercise, and to a lesser extent 24 h post‐exercise.High‐glucose ingestion 3 h post‐exercise leads to greater postprandial blood glucose, non‐esterified fatty acids, and fat oxidation, and a delay in the insulin response to the meal compared to control.Effects of acute exercise on muscle microvascular blood flow persist well after the cessation of exercise which may be beneficial for conditions characterized by microvascular and glycaemic dysfunction. Exercise, insulin‐infusion and low‐glucose mixed‐nutrient meal ingestion lead to increased muscle microvascular blood flow (MBF), whereas high‐glucose ingestion impairs MBF. We investigated whether prior cycling exercise could enhance postprandial muscle MBF and prevent MBF impairments induced by high‐glucose mixed‐nutrient meal ingestion. In a randomized cross‐over design, eight healthy young men ingested a high‐glucose mixed‐nutrient meal (1.1 g glucose/kg body weight; 45% carbohydrate, 20% protein and 35% fat) after an overnight fast (no‐exercise control) and 3 h and 24 h after moderate‐intensity cycling exercise (1 h at 70–75% V̇O2peak). Skeletal muscle MBF, measured directly by contrast‐enhanced ultrasound, was lower at 60 min and 120 min postprandially compared to baseline in all conditions (P < 0.05), with a greater decrease occurring from 60 min to 120 min in the control (no‐exercise) condition only (P < 0.001). Despite this meal‐induced decrease, MBF was still markedly higher compared to control in the 3 h post‐exercise condition at 0 min (pre‐meal; 74%, P = 0.004), 60 min (112%, P = 0.002) and 120 min (223%, P < 0.001), and in the 24 h post‐exercise condition at 120 min postprandially (132%, P < 0.001). We also report that in the 3 h post‐exercise condition postprandial blood glucose, non‐esterified fatty acids (NEFAs), and fat oxidation were substantially elevated, and the insulin response to the meal delayed compared to control. This probably reflects a combination of increased post‐exercise exogenous glucose appearance, substrate competition, and NEFA‐induced insulin resistance. We conclude that prior cycling exercise elicits long‐lasting effects on muscle MBF and partially mitigates MBF impairments induced by high‐glucose mixed‐nutrient meal ingestion. Key points: Exercise, insulin‐infusion and low‐glucose mixed‐nutrient meal ingestion increases muscle microvascular blood flow which in part facilitates glucose delivery and disposal. In contrast, high‐glucose ingestion impairs muscle microvascular blood flow which may contribute to impaired postprandial metabolism.We investigated the effects of prior cycling exercise on postprandial muscle microvascular blood flow responses to a high‐glucose mixed‐nutrient meal ingested 3 and 24 h post‐exercise.Prior exercise enhanced muscle microvascular blood flow and mitigated microvascular impairments induced by a high‐glucose mixed meal ingested 3 h post‐exercise, and to a lesser extent 24 h post‐exercise.High‐glucose ingestion 3 h post‐exercise leads to greater postprandial blood glucose, non‐esterified fatty acids, and fat oxidation, and a delay in the insulin response to the meal compared to control.Effects of acute exercise on muscle microvascular blood flow persist well after the cessation of exercise which may be beneficial for conditions characterized by microvascular and glycaemic dysfunction. [ABSTRACT FROM AUTHOR]

Key points: AMP‐activated protein kinase (AMPK) is considered a major regulator of skeletal muscle metabolism during exercise.However, we previously showed that, although AMPK activity increases by 8–10‐fold during ∼120 min of exercise at ∼65% V̇O2peak in untrained individuals, there is no increase in these individuals after only 10 days of exercise training (longitudinal study).In a cross‐sectional study, we show that there is also a lack of activation of skeletal muscle AMPK during 120 min of cycling exercise at 65% V̇O2peak in endurance‐trained individuals.These findings indicate that AMPK is not an important regulator of exercise metabolism during 120 min of exercise at 65% V̇O2peak in endurance trained men.It is important that more energy is directed towards examining other potential regulators of exercise metabolism. AMP‐activated protein kinase (AMPK) is considered a major regulator of skeletal muscle metabolism during exercise. Indeed, AMPK is activated during exercise and activation of AMPK by 5‐aminoimidazole‐4‐carboxyamide‐ribonucleoside (AICAR) increases skeletal muscle glucose uptake and fat oxidation. However, we have previously shown that, although AMPK activity increases by 8–10‐fold during ∼120 min of exercise at ∼65% V̇O2peak in untrained individuals, there is no increase in these individuals after only 10 days of exercise training (longitudinal study). In a cross‐sectional study, we examined whether there is also a lack of activation of skeletal muscle AMPK during 120 min of cycling exercise at 65% V̇O2peak in endurance‐trained individuals. Eleven untrained (UT; V̇O2peak = 37.9 ± 5.6 ml.kg−1 min−1) and seven endurance trained (ET; V̇O2peak = 61.8 ± 2.2 ml.kg−1 min−1) males completed 120 min of cycling exercise at 66 ± 4% V̇O2peak (UT: 100 ± 21 W; ET: 190 ± 15 W). Muscle biopsies were obtained at rest and following 30 and 120 min of exercise. Muscle glycogen was significantly (P < 0.05) higher before exercise in ET and decreased similarly during exercise in the ET and UT individuals. Exercise significantly increased calculated skeletal muscle free AMP content and more so in the UT individuals. Exercise significantly (P < 0.05) increased skeletal muscle AMPK α2 activity (4‐fold), AMPK αThr172 phosphorylation (2‐fold) and ACCβ Ser222 phosphorylation (2‐fold) in the UT individuals but not in the ET individuals. These findings indicate that AMPK is not an important regulator of exercise metabolism during 120 min of exercise at 65% V̇O2peak in endurance trained men. Key points: AMP‐activated protein kinase (AMPK) is considered a major regulator of skeletal muscle metabolism during exercise.However, we previously showed that, although AMPK activity increases by 8–10‐fold during ∼120 min of exercise at ∼65% V̇O2peak in untrained individuals, there is no increase in these individuals after only 10 days of exercise training (longitudinal study).In a cross‐sectional study, we show that there is also a lack of activation of skeletal muscle AMPK during 120 min of cycling exercise at 65% V̇O2peak in endurance‐trained individuals.These findings indicate that AMPK is not an important regulator of exercise metabolism during 120 min of exercise at 65% V̇O2peak in endurance trained men.It is important that more energy is directed towards examining other potential regulators of exercise metabolism. [ABSTRACT FROM AUTHOR]

Skeletal muscle and extracellular vesicle (EV) miRNA expression increases following acute endurance exercise. However, research to date has only been performed in males. The aim of this study was to describe the expression levels of a subset of miRNAs in EVs following acute exercise and compare it to skeletal muscle miRNA expression. Twelve males (age 22.9 ± 2.6 years, mean ± SD) and eight females (age 23.0 ± 3.4 years) cycled for 60 min at 70% VO2peak. Muscle biopsies and blood samples were collected at rest, immediately after and 3 hr after exercise. Acute exercise did not significantly alter the expression of miR‐1, miR‐16, miR‐23b and miR‐133a/b in EVs in males and females combined. There were no correlations between EV and skeletal muscle miRNA expression in any of the measured species at any time point. Exploratory analysis revealed differential miRNA responses to exercise between males and females. In males, a weak negative correlation was observed between skeletal muscle and EV miR‐16 expression immediately following exercise; however, the physiological relevance of this correlation is unknown. Additionally, when compared with values at rest, male skeletal muscle miR‐16 expression significantly increased immediately following exercise, whereas miR‐133a expression significantly decreased 3 hr post exercise. Our findings suggest that miRNAs isolated from EVs are not a proxy for skeletal muscle miRNA content. Our exploratory data is the first known evidence of sex‐specific differences in the miRNA response to an acute bout of endurance exercise, particularly for miRNA species implicated in mitochondrial metabolism and angiogenesis. [ABSTRACT FROM AUTHOR]

We investigated the relationship between markers of mitochondrial biogenesis, cell signaling, and antioxidant enzymes by depleting skeletal muscle glutathione with diethyl maleate (DEM) which resulted in a demonstrable increase in oxidative stress during exercise. Animals were divided into six groups: (1) sedentary control rats; (2) sedentary rats + DEM; (3) exercise control rats euthanized immediately after exercise; (4) exercise rats + DEM; (5) exercise control rats euthanized 4 h after exercise; and (6) exercise rats + DEM euthanized 4 h after exercise. Exercising animals ran on the treadmill at a 10% gradient at 20 m/min for the first 30 min. The speed was then increased every 10 min by 1.6 m/min until exhaustion. There was a reduction in total glutathione in the skeletal muscle of DEM treated animals compared to the control animals ( P < 0.05). Within the control group, total glutathione was higher in the sedentary group compared to after exercise ( P < 0.05). DEM treatment also significantly increased oxidative stress, as measured by increased plasma F2-isoprostanes ( P < 0.05). Exercising animals given DEM showed a significantly greater increase in peroxisome proliferator activated receptor γ coactivator-1 α (PGC-1 α) mRNA compared to the control animals that were exercised ( P < 0.05). This study provides novel evidence that by lowering the endogenous antioxidant glutathione in skeletal muscle and inducing oxidative stress through exercise, PGC-1 α gene expression was augmented. These findings further highlight the important role of exercise induced oxidative stress in the regulation of mitochondrial biogenesis. [ABSTRACT FROM AUTHOR]

Metabolic stresses associated with disease, ageing, and exercise increase the levels of reactive oxygen species (ROS) in skeletal muscle. These ROS have been linked mechanistically to adaptations in skeletal muscle that can be favourable (i.e. in response to exercise) or detrimental (i.e. in response to disease). The magnitude, duration (acute versus chronic), and cellular origin of the ROS are important underlying factors in determining the metabolic perturbations associated with the ROS produced in skeletal muscle. In particular, insulin resistance has been linked to excess ROS production in skeletal muscle mitochondria. A chronic excess of mitochondrial ROS can impair normal insulin signalling pathways and glucose disposal in skeletal muscle. In contrast, ROS produced in skeletal muscle in response to exercise has been linked to beneficial metabolic adaptations including mitochondrial biogenesis and muscle hypertrophy. Moreover, unlike insulin resistance, exercise-induced ROS appears to be primarily of non-mitochondrial origin. The present review summarizes the diverse ROS-targeted metabolic outcomes associated with insulin resistance versus exercise in skeletal muscle, thus, presenting two contrasting perspectives of pathologically harmful versus physiologically beneficial ROS. Here, we discuss the key sites of ROS production during exercise and the effect of ROS in skeletal muscle of people with type 2 diabetes. [ABSTRACT FROM AUTHOR]

Reduced activation of exercise responsive signalling pathways have been reported in response to acute exercise after training; however little is known about the adaptive responses of the mitochondria. Accordingly, we investigated changes in mitochondrial gene expression and protein abundance in response to the same acute exercise before and after 10-d of intensive cycle training. Nine untrained, healthy participants (mean±SD; VO2peak 44.1±17.6 ml/kg/min) performed a 60 min bout of cycling exercise at 164±18 W (72% of pre-training VO2peak). Muscle biopsies were obtained from the vastus lateralis muscle at rest, immediately and 3 h after exercise. The participants then underwent 10-d of cycle training which included four high-intensity interval training sessions (6×5 min; 90-100% VO2peak) and six prolonged moderate-intensity sessions (45-90 min; 75% VO2peak). Participants repeated the pre-training exercise trial at the same absolute work load (64% of pretraining VO2peak). Muscle PGC1-α mRNA expression was attenuated as it increased by 11- and 4-fold (P<0.001) after exercise pre- and post-training, respectively. PGC1-α protein expression increased 1.5 fold (P<0.05) in response to exercise pretraining with no further increases after the post-training exercise bout. RIP140 protein abundance was responsive to acute exercise only (P<0.01). COXIV mRNA (1.6 fold; P<0.01) and COXIV protein expression (1.5 fold; P<0.05) were increased by training but COXIV protein expression was decreased (20%; P<0.01) by acute exercise pre- and post-training. These findings demonstrate that short-term intensified training promotes increased mitochondrial gene expression and protein abundance. Furthermore, acute indicators of exercise-induced mitochondrial adaptation appear to be blunted in response to exercise at the same absolute intensity following short-term training. [ABSTRACT FROM AUTHOR]

Supplemental digital content is available in the text. Purpose: Whole-body vibration (WBV) therapy has been reported to potentially act as an exercise mimetic by improving muscle function and exercise capacity in a variety of healthy and clinical populations. Considering the important role that microvascular blood flow plays in muscle metabolism and exercise capacity, we investigated the muscle microvascular responses of acute WBV to knee extension exercise (KEX) in healthy individuals. Methods: Eleven healthy adults (age: 33 ± 2 yr; body mass index: 23.6 ± 1.1 kg·m−2) underwent 3 min of WBV, or 3 min of KEX at 25% of one-repetition maximum, in a randomized order separated by a minimum of 72 h. Femoral arterial blood flow was measured via Doppler ultrasound, and thigh muscle microvascular blood flow was measured via contrast-enhanced ultrasound at baseline and throughout the 3-min postintervention recovery period. Results: Both WBV and KEX significantly increased peak microvascular blood flow (WBV, 5.6-fold; KEX, 21-fold; both P < 0.05) during the 3-min recovery period. Despite a similar increase in femoral arterial blood flow (~4-fold; both P < 0.05 vs baseline) and whole-body oxygen consumption measured by indirect calorimetry (WBV, 48%; KEX, 60%; both P < 0.05 vs baseline) in both conditions, microvascular blood flow was stimulated to a greater extent after KEX. Conclusion: A single 3-min session of WBV in healthy individuals is sufficient to significantly enhance muscle microvascular blood flow. Despite KEX providing a more potent stimulus, WBV may be an effective method for improving microvascular blood flow in populations reported to exhibit microvascular dysfunction such as patients with type 2 diabetes. [ABSTRACT FROM AUTHOR]

Recent research highlights the importance of redox signalling pathway activation by contraction-induced reactive oxygen species (ROS) and nitric oxide (NO) in normal exercise-related cellular and molecular adaptations in skeletal muscle. In this review, we discuss some potentially important redox signalling pathways in skeletal muscle that are involved in acute and chronic responses to contraction and exercise. Specifically, we discuss redox signalling implicated in skeletal muscle contraction force, mitochondrial biogenesis and antioxidant enzyme induction, glucose uptake and muscle hypertrophy. Furthermore, we review evidence investigating the impact of major exogenous antioxidants on these acute and chronic responses to exercise. Redox signalling pathways involved in adaptive responses in skeletal muscle to exercise are not clearly elucidated at present, and further research is required to better define important signalling pathways involved. Evidence of beneficial or detrimental effects of specific antioxidant compounds on exercise adaptations in muscle is similarly limited, particularly in human subjects. Future research is required to not only investigate effects of specific antioxidant compounds on skeletal muscle exercise adaptations, but also to better establish mechanisms of action of specific antioxidants in vivo . Although we feel it remains somewhat premature to make clear recommendations in relation to application of specific antioxidant compounds in different exercise settings, a bulk of evidence suggests that N-acetylcysteine (NAC) is ergogenic through its effects on maintenance of muscle force production during sustained fatiguing events. Nevertheless, a current lack of evidence from studies using performance tests representative of athletic competition and a potential for adverse effects with high doses (>70 mg/kg body mass) warrants caution in its use for performance enhancement. In addition, evidence implicates high dose vitamin C (1 g/day) and E (≥260 IU/day) supplementation in impairments to some skeletal muscle cellular adaptations to chronic exercise training. Thus, determining the utility of antioxidant supplementation in athletes likely requires a consideration of training and competition periodization cycles of athletes in addition to type, dose and duration of antioxidant supplementation. [ABSTRACT FROM AUTHOR]

Aim/hypothesis Skeletal muscle insulin resistance and oxidative stress are characteristic metabolic disturbances in people with type 2 diabetes. Studies in insulin resistant rodents show an improvement in skeletal muscle insulin sensitivity and oxidative stress following antioxidant supplementation. We therefore investigated the potential ameliorative effects of antioxidant ascorbic acid (AA) supplementation on skeletal muscle insulin sensitivity and oxidative stress in people with type 2 diabetes. Methods Participants with stable glucose control commenced a randomized cross-over study involving four months of AA (2×500 mg/day) or placebo supplementation. Insulin sensitivity was assessed using a hyperinsulinaemic, euglycaemic clamp coupled with infusion of 6,6-D 2 glucose. Muscle biopsies were measured for AA concentration and oxidative stress markers that included basal measures (2′,7′-dichlorofluorescin [DCFH] oxidation, ratio of reduced-to-oxidized glutathione [GSH/GSSG] and F 2 -Isoprostanes) and insulin-stimulated measures (DCFH oxidation). Antioxidant concentrations, citrate synthase activity and protein abundances of sodium-dependent vitamin C transporter 2 (SVCT2), total Akt and phosphorylated Akt (ser473) were also measured in muscle samples. Results AA supplementation significantly increased insulin-mediated glucose disposal (delta rate of glucose disappearance; ∆Rd) ( p =0.009), peripheral insulin-sensitivity index ( p =0.046), skeletal muscle AA concentration ( p =0.017) and muscle SVCT2 protein expression ( p =0.008); but significantly decreased skeletal muscle DCFH oxidation during hyperinsulinaemia ( p =0.007) when compared with placebo. Total superoxide dismutase activity was also lower following AA supplementation when compared with placebo ( p =0.006). Basal oxidative stress markers, citrate synthase activity, endogenous glucose production, HbA1 C and muscle Akt expression were not significantly altered by AA supplementation. Conclusions/interpretation In summary, oral AA supplementation ameliorates skeletal muscle oxidative stress during hyperinsulinaemia and improves insulin-mediated glucose disposal in people with type 2 diabetes. Findings implicate AA supplementation as a potentially inexpensive, convenient, and effective adjunct therapy in the treatment of insulin resistance in people with type 2 diabetes. [ABSTRACT FROM AUTHOR]

Background It is clear that reactive oxygen species (ROS) produced during skeletal muscle contraction have a regulatory role in skeletal muscle adaptation to endurance exercise. However, there is much controversy in the literature regarding whether attenuation of ROS by antioxidant supplementation can prevent these cellular adaptations. Therefore, the aim of this study was to determine whether vitamin C and E supplementation attenuates performance and cellular adaptations following acute endurance exercise and endurance training. Methods A double-blinded, placebo-controlled randomized control trial was conducted in eleven healthy young males. Participants were matched for peak oxygen consumption (VO 2 peak) and randomly allocated to placebo or antioxidant (vitamin C (2×500 mg/day) and E (400 IU/day)) groups. Following a four-week supplement loading period, participants completed acute exercise (10×4 min cycling at 90% VO 2 peak, 2 min active recovery). Vastus lateralis muscle samples were collected pre-, immediately-post- and 3 h-post-exercise. Participants then completed four weeks of training (3 days/week) using the aforementioned exercise protocol while continuing supplementation. Following exercise training, participants again completed an acute exercise bout with muscle biopsies. Results Acute exercise tended to increase skeletal muscle oxidative stress as measured by oxidized glutathione (GSSG) ( P =0.058) and F 2 -isoprostanes ( P =0.056), with no significant effect of supplementation. Acute exercise significantly increased mRNA levels of peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), mitochondrial transcription factor A (TFAM) and PGC related coactivator (PRC), with no effect of supplementation. Following endurance training, supplementation did not prevent significantly increased VO 2 peak, skeletal muscle levels of citrate synthase activity or mRNA or protein abundance of cytochrome oxidase subunit 4 (COX IV) ( P <0.05). However, following training, vitamin C and E supplementation significantly attenuated increased skeletal muscle superoxide dismutase (SOD) activity and protein abundance of SOD2 and TFAM. Conclusion Following acute exercise, supplementation with vitamin C and E did not attenuate skeletal muscle oxidative stress or increased gene expression of mitochondrial biogenesis markers. However, supplementation attenuated some (SOD, TFAM) of the increased skeletal muscle adaptations following training in healthy young men. [ABSTRACT FROM AUTHOR]

Antioxidant vitamin C (VC) supplementation is of potential clinical benefit to individuals with skeletal muscle oxidative stress. However, there is a paucity of data reporting on the bioavailability of high-dose oral VC in human skeletal muscle. We aimed to establish the time course of accumulation of VC in skeletal muscle and plasma during high-dose VC supplementation in healthy individuals. Concurrently we investigated the effects of VC supplementation on expression levels of the key skeletal muscle VC transporter sodium-dependent vitamin C transporter 2 (SVCT2) and intramuscular redox and mitochondrial measures. Eight healthy males completed a randomized placebo-controlled, crossover trial involving supplementation with ascorbic acid (2×500 mg/day) over 42 days. Participants underwent muscle and blood sampling on days 0, 1, 7, and 42 during each treatment. VC supplementation significantly increased skeletal muscle VC concentration after 7 days, which was maintained at 42 days (VC 3.0±0.2 (mean±SEM) to 3.9±0.4 mg/100 g wet weight (ww) versus placebo 3.1±0.3 to 2.9±0.2 mg/100 g ww, p =0.001). Plasma VC increased after 1 day, which was maintained at 42 days (VC 61.0±6.1 to 111.5±10.4 µmol/L versus placebo 60.7±5.3 to 59.2±4.8 µmol/L, p <0.001). VC supplementation significantly increased skeletal muscle SVCT2 protein expression (main treatment effect p =0.006) but did not alter skeletal muscle redox measures or citrate synthase activity. A main finding of our study was that 7 days of high-dose VC supplementation was required to significantly increase skeletal muscle vitamin C concentration in healthy males. Our findings implicate regular high-dose vitamin C supplementation as a means to safely increase skeletal muscle vitamin C concentration without impairing intramuscular ascorbic acid transport, antioxidant concentrations, or citrate synthase activity. [ABSTRACT FROM AUTHOR]

Abstract: Background: Maintaining skeletal muscle mitochondrial content and function is important for sustained health throughout the lifespan. Exercise stimulates important key stress signals that control skeletal mitochondrial biogenesis and function. Perturbations in mitochondrial content and function can directly or indirectly impact skeletal muscle function and consequently whole-body health and wellbeing. Scope of review: This review will describe the exercise-stimulated stress signals and molecular mechanisms positively regulating mitochondrial biogenesis and function. It will then discuss the major myopathies, neuromuscular diseases and conditions such as diabetes and ageing that have dysregulated mitochondrial function. Finally, the impact of exercise and potential pharmacological approaches to improve mitochondrial function in diseased populations will be discussed. Major conclusions: Exercise activates key stress signals that positively impact major transcriptional pathways that transcribe genes involved in skeletal muscle mitochondrial biogenesis, fusion and metabolism. The positive impact of exercise is not limited to younger healthy adults but also benefits skeletal muscle from diseased populations and the elderly. Impaired mitochondrial function can directly influence skeletal muscle atrophy and contribute to the risk or severity of disease conditions. Pharmacological manipulation of exercise-induced pathways that increase skeletal muscle mitochondrial biogenesis and function in critically ill patients, where exercise may not be possible, may assist in the treatment of chronic disease. General significance: This review highlights our understanding of how exercise positively impacts skeletal muscle mitochondrial biogenesis and function. Exercise not only improves skeletal muscle mitochondrial health but also enables us to identify molecular mechanisms that may be attractive targets for therapeutic manipulation. This article is part of a Special Issue entitled Frontiers of mitochondrial research. [Copyright &y& Elsevier]

Abstract: Skeletal muscle mitochondrial dysfunction is believed to play a role in the progression and severity of amyotrophic lateral sclerosis (ALS). The regulation of transcriptional co-activators involved in mitochondrial biogenesis and function in ALS is not well known. When compared with healthy control subjects, patients with ALS, but not neurogenic disease (ND), had lower levels of skeletal muscle peroxisome proliferator-activated receptor γ coactivator-1α (PGC-1α) mRNA and protein and estrogen-related receptor-α (ERRα) and mitofusin-2 (Mfn2) mRNA. PGC-1β, nuclear respiratory factor-1 (NRF-1) and Mfn1 mRNA as well as cytochrome C oxidase subunit IV (COXIV) mRNA and protein were lower in patients with ALS and ND. Both patient groups had reductions in citrate synthase and cytochrome c oxidase activity. Similar observations were made in skeletal muscle from transgenic ALS G93A transgenic mice. In vitro, PGC-1α and PGC-1β regulated Mfn1 and Mfn2 in an ERRα-dependent manner. Compared to healthy controls, miRNA 23a, 29b, 206 and 455 were increased in skeletal muscle of ALS patients. miR-23a repressed PGC-1α translation in a 3′ UTR dependent manner. Transgenic mice over expressing miR-23a had a reduction in PGC-1α, cytochome-b and COXIV protein levels. These results show that skeletal muscle mitochondrial dysfunction in ALS patients is associated with a reduction in PGC-1α signalling networks involved in mitochondrial biogenesis and function, as well as increases in several miRNAs potentially implicated in skeletal muscle and neuromuscular junction regeneration. As miR-23a negatively regulates PGC-1α signalling, therapeutic inhibition of miR-23a may be a strategy to rescue PGC-1α activity and ameliorate skeletal muscle mitochondrial function in ALS. [Copyright &y& Elsevier]